The present invention relates to suspensions, having a high storage stability, comprising an aqueous silicate solution and filler material.
Such a suspension is for instance disclosed in U.S. Pat. No. 4,361,659. Said suspension comprises crystalline calcium carbonate and quartz powder as fillers. To obtain a reasonable stability, an alkali resistant organic polymer is included in the suspension.
Organic chemicals are frequently not desirable in environmentally/health sensitive applications. Safety can be a serious issue when applied in the proximity of higher temperature equipment, e.g. when dried at higher temperatures. Furthermore, suspensions stabilized with organic stabilizers are also very sensitive to small variations in composition. For instance they may turn into gels during storage in case of slight overdosing of the stabilizing agent. Further suspensions stabilized with organic compounds are often not stable any more when only slightly diluted or at a different ionic strength of the aqueous phase.
In U.S. Pat. No. 4,403,059, a composition is described based upon an aqueous solution of alkali metal silicate with a content from 10 to 40% by weight of a powdered inorganic filler, having a good storage stability by using at least one zinc soap of a fatty acid, having from 12 to 22 carbon atoms as a stabilizer. With the composition according to this US-patent specification it is difficult to define the specific amount of organic stabilizer needed for optimum control of the stability, without excessively increasing the viscosity.
Furthermore the use of stabilizers containing zinc soap and polymers limits the possible application areas of such a suspension as a result of environmental and safety requirements.
Suspensions may also be stabilized with inorganic stabilizers as inorganic clays, with particles of around 0.1 micrometer in diameter, which clays are also used as thickeners, having swelling properties. Further these stabilizers may interfere with other components used in the specific composition.
Suspensions stabilized with inorganic stabilizers have generally high viscosities, due to the thickening properties of the stabilizer, which limits the applicability as well as the level of solids, that can be added.
In this respect reference is made to GB-A-2 058 818, in which an aqueous spray coating adhesive composition is disclosed comprising (i) a solution of an alkali metal silicate (ii) 1 to 10% by weight of finely divided inorganic powder containing, mineralogically, more than 15% kaolinite and (iii) finely divided silica. The silica is preferably included in the form of silicic acid. In this patent application, the kaolinite clay is used as filler/stabilizer. The total amount of fine filler material is limited to a maximum of 10% by weight.
At present it is not known how to manufacture aqueous silicate suspensions including relatively high amounts of fine filler materials, yet maintaining a sufficient storage stability in the absence of a stabilizer.
The present invention now provides a suspension having high storage stability, comprising an aqueous silicate solution and a filler material, wherein the silicate solution has a silicate content of at least 20% by weight, the filler material has an average particle size of 0.8-15 xcexcm and a specific weight of below 2.75 kg/l, the filler being chosen from the group consisting of a) zeolites, b) fine particulate or fibrous amorphous inorganic material being relatively inert in an alkaline aqueous solution, comprising amorphous alkali metal alumino silicate c) fine particulate of graphite or carbon black, or d) mixtures thereof, said suspension having a high storage stability in the absence of a stabilizer. It is deemed surprising that the suspensions according to the invention have excellent storage stability in the absence of a stabilizer. Usually no settling of the fine filler material will take place within five days in a liquid column with a height of 24 cm. Preferably the specific weight of the filler material is below 2,5 kg/l.
It is noted that with the suspension according to the invention the use of stabilizers is by no means excluded, as it may sometimes for specific applications be advantageous to add a stabilizer e.g. to improve the stability of the suspension even further.
In the prior art aqueous silicate solutions are used for many applications where filling or binding properties are required. For instance leaking sewer pipes can be repaired in the ground by pumping a concentrated aqueous silicate solution into the leaking sewer system. Said silicate solution leaks out of this system filling up the space in the ground around the leaking locations. After some time the silicate in the sewer system is replaced by a hardener which also leaks into the leaking locations and the surrounding ground neutralizing the silicate and thus sealing the leaks. The silicate and the hardener thus fill up the space between the ground particles around the leaks.
Usually hardeners in the form of relatively expensive esters of organic acids are used, which hydrolyse and thereby release an acid which is needed for neutralization of the silicate.
It is of environmental and economic importance to minimize the amount of ester (and consequently of the silicate, needing neutralization) required.
The presence of the filler material in the suspension according to the invention has the advantage that for instance in the application of sewer system repair, this filler material may partially fill up the spaces between the ground particles, which reduces the amount of silicate needed and consequently also reduces the amount of ester needed. Moreover some of the pores in the ground will be blocked by the filler which reduces the penetration of silicate and ester into the ground, thus further reducing the amount of silicate and ester required. Also the solids content of the suspension is increased, thereby further increasing the density and the strength of the material filling up the pores in the ground and consequently further reducing the permeability of the layer around the leaking locations of the sewer system.
Usually in silicate liquors which are used for sewage system repair the SiO2 content is limited to maximum about 33% by weight, which of course limits the amount of silica in silicagel (Dry Solids content), which can be formed by addition of the hardener. This limited solids content has a major influence on the physical and mechanical properties of the gel which can be obtained, limiting the density, strength and also limiting the attainable minimum for the permeability of the bound material, like sand, ground or soil. Also the hydrolysis of the ester into the acid can be relatively slow and uncontrolled.
As filler in the suspension according to the present invention advantageous zeolites are used. Zeolites are crystalline aluminosilicates.
Most zeolites are well known relatively inert environmentally harmless substances. Examples of zeolites, that are available or can be produced in fine particulate form are zeolites 4A, zeolite P, zeolite X and zeolite Y. Zeolite P is preferred, because of its layered structure, being non abrasive and relatively soft, also implicating less wear in machinery.
A suspension according to the present invention comprising synthetically produced zeolite P can be made, having the additional advantage of not containing carcinogenic crystalline silica (quartz, cristobalite) as can be the case when inorganic mineral fillers are applied. These crystalline silicas are declared to be carcinogenic, and it is to be expected, that the use thereof will be prohibited or restricted globally.
It is preferred to use zeolite P, prepared according to the method described in EP-B-0 384 070, having a silicon to aluminium ratio of not higher than 1,33, and a calcium binding capacity as defined in EP-B-0 384 070 of at least 150 mg CaO per g anhydrous aluminosilicate.
The filler material may advantageously comprise a fine particulate or fibrous amorphous inorganic material, being relatively inert in an alkaline aqueous solution, comprising an amorphous alkali metal-aluminosilicate. Most amorphous products tend to be too reactive in the alkaline silicate environment. The exception is found to be amorphous sodium aluminosilicate, produced by precipitation from a highly alkaline aluminate solution and a highly alkaline silicate solution.
A preferred example of such amorphous filler material is of synthetic origin, as in natural alkali metal aluminosilicates, trace amounts of crystalline silica may again be present, implicating a restricted future use thereof as is outlined above. Synthetic alkali metal aluminosilicate is free of crystalline silica when produced from purified liquid raw materials (silicate and aluminate).
The filler may be a mixture of the above mentioned zeolites, fibrous or particulate amorphous inorganic material, graphite or carbon black.
The inorganic filler material used in the suspension according to the invention preferably comprises a zeolite.
The maximum particle size of the filler material is of course depending on the specific weight of filler material, the shape of the filler material and the specific weight of the silicate liquor, the molar ratio (SiO2/M2O) and the concentration of the alkali metal silicate in the silicate solution in order to provide a suspension having the required storage stability.
For highly porous particles with a very open structure as for example amorphous sodium-aluminosilicate the average particle size can be as high as 14.83 micrometers still providing a suspension with reasonable stability. However, advantageously the average particle size of the filler material is comprised between 0.8-10 xcexcm, preferably between 0.8-5 xcexcm, more preferably between 0.8-4 xcexcm, and most preferably between 0.8-2 xcexcm.
The content of the filler material will have its physical limitations in the suspension. Preferably the content of the filler material in the suspension is such, that the suspension is pourable or pumpable, which is a requirement for specific applications. For other applications (e.g.: for adhesion of paper, wood, concrete or bricks) more concentrated suspensions with a higher viscosity will be required. Preferably the content of the filler material is comprised between 2-50% by weight, more preferably between 10-40% by weight, and even more preferably between 10-30% by weight.
In the suspension according to the invention the aqueous silicate solution is not specifically limited and can be selected from known silicate solutions depending on the specific application requirements. Usually the silicate solution is an alkali metal silicate solution, i.e. Na-, K-, or Li- silicate solutions or an ammonium silicate solution or mixtures thereof.
In the present specification the SiO2/M2O molar ratio of the silicate will be used as a measure to identify the specific silicate solution, wherein M designates the specific alkali metal or ammonium (Na, K, Li, NH4).
The SiO2/M2O molar ratio of these soluble silicates can vary from 1.0 to around 4.0 and for lithium silicate even higher. All silicate solutions are alkaline, but the alkalinity decreases with increasing molar ratio. Consequently silicate solutions with higher molar ratios are safer in handling, which is demonstrated by the following safety classification of the standard silicate solutions as offered on the market.
The preferred SiO2/M2O ratio for most applications is therefore above 2.6 and more preferably 3.3 and higher for safety reasons. For these applications requiring hardening it is also preferred to maximize the SiO2 content and consequently also the SiO2/M2O ratio to minimize the amount of hardener required for neutralization. It was surprisingly also found, that a higher molar ratio is also more suitable to produce stable suspensions.
The properties of the suspension are highly influenced by the SiO2/M2O molar ratio. Therefore advantageously the SiO2/M2O molar ratio of the aqueous silicate solution is comprised between 1-4.5, preferably between 2-4.2 and most preferably between 2.6-4.2.
The silicate content of the aqueous silicate solution used in the suspension according to the invention is at least 20% by weight and in particular at least 25% by weight. Preferably the silicate content is as high as possible.
The invention further provides an adhesive composition comprising a suspension according to the invention. Such adhesive compositions can be used for all kinds of adhesion purposes e.g. paper, wood, concrete, bricks, floor tiles, rubber, leather (e.g. shoes), glass, metal (e.g. aluminium foil), plywood, plasterboard and woodchip manufacture etc. Especially materials with irregular surfaces which are usually difficult to adhere, like filter paper, wood or concrete can be adhered to each other or other surfaces by use of such an adhesive. The adhesive is particularly suitable for bonding of perlite, vermiculite, glass fibre, mineral fibre, rockwool, for e.g. thermal or acoustic insulation in blankets, panels, boards, shapes, inserts, spray-on coatings and the like. The suspension according to the invention causes a very fast tack and dries relatively quickly gives a flexible bond and significantly reduces dusting.
Advantages of the use of suspensions according to the invention in adhesive compositions are a.o.: xe2x80x94There are no organic compounds (incl. volatile solvents) used. xe2x80x94There is no necessity to clean or dry the surfaces before using the silicate suspension as filler or adhesive and the (inorganic) adhesive or filler reduces the flammability of the materials used.
Because of the absence of the organic compound materials, which themselves are safe and are bonded by adhesives according to the invention (e.g. paper, cardboard, wood, sand, soil, etc.) may be safely disposed of by landfill.
The SiO2/M2O molar ratio of the aqueous silicate solution of the adhesive according to the present invention, M being alkali metal or ammonium, is preferably comprised between 2.8 and 4.2. Higher molar ratio mostly leads to viscous products. These viscous products can however still be used as adhesives and may be, if required, diluted in order to reduce the viscosity. The average particle size is preferably below 3 xcexcm.
A preferred example of a suspension according to the invention which is suitable as an adhesive is a suspension of zeolite Zeocros CG180 of Crosfield (Eijsden, The Netherlands) in a 10% to 30% % by weight suspension thereof in neutral silicate containing around 35% by weight of silicate with a molar ratio of about 3.3, the average particle size of the Zeocros CG180 being about 1 xcexcm. If a small amount of such a suspension is spread over a part of a surface of a paper sheet and then covered with another paper sheet, it was found, that an immediate strong tack was obtained and that drying took place under normal conditions at approximately 20xc2x0 C. within a few minutes. Strong binding between the bound paper parts was realized for filter paper as well as for standard paper and the paper parts could not be separated without tearing. By use of the adhesive according to the invention a reduced flammability of the bound paper parts is obtained, no organic compounds are used and a better binding is obtained.
With adhesives, according to the invention laminated paper, like spirally wound laminated paper tubes, cardboard, corrugated cardboard, wall-paper, laminated wood, plywood, leather, e.g. shoe soles and building materials can be manufactured. It was observed that for the adhesion of bricks and shoe soles, the use of suspensions of zeolite Zeocros CG180 with higher zeolite contents (e.g. 27%) were giving stronger binding and are therefore preferred. The adhesive can also be used to bind powders or other particulate or fibrous materials to form larger agglomerates, e.g. for the production of structural building components, like bricks, roof tiles etc. Also it can be used for the preparation of paper-mache for manufacturing paper articles.
Adhesives according to the invention can also be used to bind stones, bricks or concrete building materials for the construction of walls, houses and also for repairing shoes and shoe soles, by adhesion of leather components.
It was found, that for these applications as adhesive, addition of a surfactant or a hardener was not necessary as long as there is sufficient porosity in the material bound together to allow penetration of the adhesive and to allow the suspension to dry. However in case evaporation of the water present in the suspension is too slow or if better water resistance is required, a hardener and/or a surfactant can be added. As surfactants, cationic surfactants like cetyltetra ammoniumchloride may be preferred.
The invention further provides a drilling fluid comprising a suspension according to the invention. In oil well drilling, suspensions of various solids in an aqueous system are cycled through the bore hole, which suspensions are called drilling fluid or drilling mud. The main functions of said fluid is cooling of the drill head and removal of the cuttings.
The purpose of said solids used in a drilling fluid is to increase the density of the drilling fluid and to penetrate the pores in the ground around the bore hole to block these pores and to minimize losses of drilling fluid into the surrounding formation. In practice these solids have presented problems, as they may tend to settle, which can occur during interruption of the drilling operation e.g. during connection of a new length of drilling pipe etc. In the field of drilling silicate is already used to increase the density of the drilling fluid and to assist in the removal of the cuttings.
A high density of the drilling fluid is necessary to avoid so called xe2x80x9cblow outsxe2x80x9d in case a layer is reached in the formation having a high pressure.
The use of the suspension according to the invention as a drilling fluid will however have a number of additional advantages. Easy and safe dosing of particles, already in suspended form (no dust) is obtained, which is safe for health and environment (the fluid does not contain any crystalline silicas nor any other toxic or environmentally unsafe component). The suspended particles can be selected easily so as to have the right size for blocking the pores in the ground. Two essential components for drilling can be simultaneously dosed in one liquid. As the average particle size can be adjusted easily, the risk of settling of particles in the drilling fluid is substantially eliminated.
Due to environmental reasons, drilling fluids which contained high levels of organic compounds in the past for various reasons are now being replaced by xe2x80x9cAqueous Drilling Fluidsxe2x80x9d, being free or practically free of organic compounds. A problem related to this change is lubrication of the bore head, which was realized in the past by the addition of organic lubricants, which are not acceptable nowadays.
The use of a stable suspension containing graphite or carbon black provides a good solution to the lubrication problem, connected to the use of xe2x80x9cAqueous Drilling Fluidsxe2x80x9d, where it is not practical to mix in fine dusty powder of graphite or carbon black in a drilling fluid on a windy outside or off-shore rigs.
The invention further provides a sewer renovation fluid comprising a suspension according to the invention. As discussed earlier the suspension according to the invention can be used in a sewer renovation fluid which provides the following advantageous properties. The solid content in the silicate suspension used is much higher than in the previous known suspensions whereby the filling of the space between soil particles in the ground is improved, leading to a denser and stronger sealing layer around the leaking location and a longer additional life for the repaired sewer part. Further less permeability of the layer around the repaired sewer part is obtained which further minimizes leakage of fluid from the sewer system to the environment or of ground water into the sewer system. A better efficiency and less leakage of the suspension used for repair into the ground is obtained. This can be a very important advantage as in highly porous ground these losses are substantial.
Finally an additional protection of the environment is obtained in case Zeocros CG180 is used, which has binding properties for several heavy metals, mineral oxides and mineral fines. Consequently in case the permeability for sewer fluid would not be 100% perfect and if very small quantities would still leak through, heavy metals could be captured by said zeolite Zeocros CG180 further preventing these from reaching the environment.
The same principle as applied in the sewer renovation system can also be applied in other systems, where leaks or cracks have to be repaired, e.g. in concrete floors, which can be important in case of (chemical-) factory floors and also in concrete tanks, protecting tanks which contain chemicals and which are placed inside the concrete tank. The system could even be applied in road repairs. where the holes or cracks can be filled up with the suspension together with the hardener. In case of larger holes, a filler material could be added, e.g. sand.
The invention also provides a binder composition comprising a suspension according to the invention. Binder applications are numerous and will of course not all be cited here. The suspension according to the invention can be used for binding particles in agglomeration and the like. The advantageous binder properties can be used in for instance sprayed concrete, the production of roof tiles or other structural building components, in foundries (sand+a binder system), in grouting, production of solid (buildingxe2x88x92or construction) blocks from various solids and silicate as a binder. In this application, solid wastes in powder form, e.g. powders from waste incineration and various fly-ashes can be used in various building applications.
The suspension according to the invention improves the density, hardness and impermeability of the manufactured products. In case of incinerated waste and fly ashes, it will also contribute to the reduced leaching out of heavy metals contained in these materials. It can also be used to bind dusty compound, e.g. mineral fines, asbestos.
Further a waste fixation composition is provided comprising a suspension according to the invention. For waste fixation several techniques are developed. An impermeable wall and an impermeable floor can be formed around the waste dump, where the waste is stored. This wall and floor usually consist of a plastic layer and/or a solidified layer, e.g. concrete.
According to the invention said wall and floor comprise a layer containing solids and silicate which is hardened by neutralisation and gelling.
By using the suspension according to the invention as a waste fixation material the following benefits are obtained.
Due to the increased solids content a harder and denser, and consequently less permeable layer will be obtained with better encapsulating properties and a potentially longer lifetime of the encapsulated material. Leaching out will substantially be eliminated by use of the suspension according to the invention.
As specified earlier the use of a zeolite of the P-type, e.g. zeolite Zeocros CG 180 will provide the additional benefit that it binds many heavy metals and also amines and ammonium ions in case there would still be some leakage.
Further a fixation and hardening composition is provided for ground surfaces (e.g.: of sand, soil or clay), comprising a suspension according to the invention. Surface fixation or hardening is applied for (country-) road preparations or to produce a harder foundation e.g for constructions etc. and is also of interest for the fixation of pure sand surfaces, e.g. dunes and deserts, which are spread or moved by the wind. According to the invention surfaces can be fixed and hardened by impregnating these surfaces (e.g. by spraying on) with a suspension according to the invention. Hardening could be realized by neutralisation by means of the carbondioxide in the air followed by gelation. However this is a slow process and alternatively a hardener can be applied, preferably based on amorphous Silica.
Further an alternative for a concrete cement composition is provided for construction works comprising a suspension according to the invention. In this application a suspension according to the invention can be mixed with a hardener (preferably Silica or an amorphous metalsilicate). In a preferred procedure for this application additional solid compounds are mixed in as well (e.g.: sand) in order to increase the strength of the hard solid obtained after hardening and to reduce costs.
The invention also provides a spray-coating composition comprising a suspension according to the invention. Spray coatings are coatings as e.g. described in GB-A-2 058 818.
A paper filler composition comprising a suspension according to the invention is provided. It was found that especially zeolites of the P-type with small particles (around 1 xcexcm) as provided by Zeocros CG180, tested in the paper industry as a potential filler, showed optimum characteristics with respect to opacity and printing properties achieved, matching the best products in the market. The paper industry however requires zeolite Zeocros CG180 to be provided in suspended form and not in powder form.
Therefore the suspension according to the invention is very suitable for that purpose.
The present invention also relates to the use of an adhesive composition comprising a suspension according to the invention for the manufacture of cellulose containing materials, like paper articles, e.g. papier-mxc3xa2chxc3xa9, laminated paper, such as cardboard, spirally or convolute (parallel) wound laminated paper tubes and drums and the like. For example, the adhesive can be used in a method for manufacturing tubes comprising two or more layers of cardboard and/or paper, wherein an adhesive is applied on at least one of the surfaces of the said layers, the layers being spirally or convolutely wound over each other, wherein an adhesive according to the present invention is applied on the said surface(s). By using the adhesive in the method for manufacturing said tubes and drums, an improved hardness and better crush strength and lower moisture content in the final tubes and drums can be obtained compared to organic adhesives used in practice (e.g.: dextrin or polyvinylacetate (PVA). Surprisingly, the production speed can be increased compared to adhesives used in the state of the art. Furthermore the same adhesive can be used to adhere the outer layer of the tubes, normally a thin paper layer, to the other layers, normally freshly made of cardboard. In the state of the art, different adhesives have to be used to adhere said thin paper layer to the outer cardboard layer on the one hand and to adhere the cardboard layers with each other on the other hand.
Paper material being coated with the adhesive according to the present invention has fire retardant properties. This is a remarkable and important feature, as paper/cardboard products made using the adhesive according to the present invention can be used at high temperatures and are safe in use and during storage. In laminated paper articles the adhesive according to the present invention may be formed as a layer between the paper layers, so that each paper layer therein has said fire retardant properties.
The suspension according to the present invention can advantageously be used as fireproof coating on all kinds of substrates which are e.g. like discussed above.
In particular the present invention also relates to the use of an adhesive composition comprising a suspension according to the invention as a binder for rockwool or glass fibre.
It will be clear that the above cited applications are not meant to be an exhaustive enumeration and that many other applications are feasible.
Advantageously the suspensions according to the invention can be hardened by using a hardener. Preferably said hardener comprises an amorphous silica, or alternatively an amorphous metal silicate, like aluminium silicate, magnesium silicate or calcium silicate.
In a preferred embodiment of the application of the suspensions according to the invention a hardener system is used based on amorphous silica.
It has surprisingly been found, that amorphous silica (SiO2) offers an excellent inorganic hardener, which can be used beneficially in combination with silicate based suspensions, according to the invention.
Amorphous silica is synthetically produced and is offered on the market by several companies, e.g. by Crosfield in Warrington (UK) under the Brandnames Gasil, Lucilite, Microsil etc. Synthetic amorphous silicas are produced by neutralisation of a silicate solution, filtering-off and washing of the Silica produced and subsequent drying.
The solubility (rate of dissolution) of the amorphous silica, obtained according to this production process, in an alkaline solution depends on the precipitation conditions and the drying conditions applied in the production process of the amorphous silica and also on the dissolution temperature and of the alkalinity of the solution used and can be varied accordingly.
It was now surprisingly found, that adding finely divided amorphous silica does not produce a stable suspension at all. On the contrary, silica in amorphous form slowly dissolves in the silicate, thus acting as an acid, neutralizing the silicate and consequently forming a gel. This is the case when sufficient amorphous silica is mixed in pure silicate liquors, giving a gel, but also when sufficient amorphous silica is mixed in suspensions according to the invention. Gels obtained when mixing amorphous silica in suspensions according to the invention provided superior density, hardness and minimum permeability.
Consequently it was found, that amorphous silica forms an ideal hardener, being again completely inorganic and completely safe with respect to safety and the environment. It also further reduces the flammability and increases the solid content after hardening. An additional benefit being, that the hardened suspension, using sufficient amorphous silica forms a neutralised solid phase with superior adhesion and filling properties, which is very strong and practically insoluble in water.
It was found, that the rate of hardening of the suspensions of zeolite in a silicate liquor, e.g. the suspension according to the invention, using amorphous silica can be influenced by the choice of amorphous silica and by the amount of amorphous silica used. The use of silicas with a higher rate of dissolution in alkaline aqueous solutions increases the hardening rate.
It is therefore possible to control the hardening (setting) rate by choosing the type of silica, the optimal concentration and the temperature, as can be carried out by a person skilled in the art. The hardener system should be mixed in the suspension shortly before use.
The use of silica as a hardener has several benefits, it further increases the solid content leading to a denser, stronger and less permeable phase. It is safe for human health and the environment and it also implies, that no organic components are required.
As a hardener, also an amorphous metal silicate can be used. Such a compound results in a spacial configuration change of the silicate in the suspension by alteration of the molar SiO2/M2O ratio thereof. Suitable metal silicates are those which do not readily dissolve in the silicate containing suspension to be hardened, like e.g. magnesium silicate, calcium silicate or aluminium silicate.
It was found, that graphite or carbon black, which are well known environmentally acceptable lubricants can be also suspended in aqueous liquors of silicate, forming stable suspensions preferably the content of the graphite particles is comprised between 1-50% by weight, preferably between 5-35% by weight.
Stable suspensions were further obtained when fine particles of zeolite and of graphite were together suspended in aqueous silicate liquors. In particular the filler material comprises a mixture of fine particles of zeolite of the P-type and of graphite or carbon black, more preferably the particulate filling material comprises a mixture of a zeolite of the P-type marketed by Crosfield under the brand name Zeocros CG 180 and graphite or carbon black.
Further a drilling fluid is provided comprising such a suspension.